Modern manufacturing processes are capable of producing objects that have nano-metric structural elements. Such inspected objects may be semiconductor wafers, reticles, solar panels and the like. An inspected surface of such an inspected object is not flat and this may result in focus errors.
Slowly developed focus errors can be compensated for by a mechanical module that can elevate or lower the inspected object. This compensation is relatively slow and is limited by mechanical constraints.
There is a growing need to provide a fast focus error correction method and an inspection system having fast focus alteration capabilities.